The performance, in particular the energy density, of electrochemical energy storage systems such as lithium-ion batteries (LIB) depends essentially on the selection and the configuration of the electrodes in the cell. Two fundamentally different methods for coating the current collector with the active material (also referred to below as active material) are discussed in the related art, namely, by applying an active material slurry (so-called slurry application process) and by applying a free-standing active material foil (see, for example, EP 1 644136, US 2015/0061176 A1, or US 2015/0062779 A1).
Patent document DE 10 2013 204 875 A1 provides a method in which a dry active material composition is applied to a current collector. In one specific embodiment, a mask is used, which is placed on the current collector prior to the coating step in order to selectively exclude areas from the covering with active material.
Patent document US 2016/0043375 A1 provides a secondary battery that includes an electrode stack that is obtained by stacking planar battery cells which include a charge layer and a lead electrode. The lead electrode may be completely enclosed by the electrodes of the battery cell.
The manufacture of electrodes from free-standing active material foils is believed to be understood from the related art and is discussed in EP 1 644136, US 2015/0061176 A1, or US 2015/0062779 A1, for example. The free-standing active material foil is produced in a solvent-free process, typically with a layer thickness of approximately 100 μm-300 μm. The free-standing foil is optionally cut to the desired size and subsequently applied to a preformed current collector. The cutting of the electrode may also take place in the laminated composite made up of the current collector and the active material foil. For manufacturing an electrochemical cell, at least one each of a cut anodic, negative electrode and a cathodic, positive electrode, divided by a separator, are packed into a housing (for example, in the form of a pouch or a solid housing (can)), and the housing is filled with an electrolyte. The electrolyte is ionically conductive, and surrounds the electrodes and the separator or penetrates into their pores.
The current collector is made of an electrically conductive material, in particular a metal, and has a flat configuration. According to the related art, the side edges of the current collector and of the active material layer are in flush alignment, or the current collector protrudes beyond the extension of the active material layer, at least on one side. The cut electrodes thus have more or less pronounced areas on each side that are made of uncoated current collector, in particular metal. To avoid an electrical short circuit within the cell, according to the related art the current collectors that protrude or that are not covered by active material are electrically insulated by targeted oxidation processes, for example. The cathodic current collector, which is often made of aluminum, may thus be insulated by the aluminum oxide that results. An alternative method uses electrically nonconductive plastics (rubber, for example) for sealing.
Alternatively, by a suitable selection of the geometries of the electrodes and of the nonconducting separator, there is also the option for configuring the cell in such a way that a short circuit is effectively prevented. The separator is configured in such a way that it protrudes beyond the edge of the electrodes, so that the electrodes are not able to come into contact with one another. This method requires precise alignment of the individual components during the stacking.
In addition to the contact of the electrodes with one another, the electrochemical cell manufactured according to the related art also entails the risk that the uncoated current collector may laterally contact the housing of the cell, and may even damage the cell over its service life. If insulation of the metal edges is dispensed with, here as well there is also the risk of an electrical short circuit.
Due to the described measures for preventing a short circuit within the cells, the portion of the volume of the cell that is not filled with active material increases and thus does not contribute to energy storage. The volumetric power density drops to the cell level.
The object of the present invention, therefore, is to provide an electrode that is protected from short circuits without a reduction in the power density of the battery cells. The aim is also to manufacture the electrode without additional method steps such as oxidation processes. This object is achieved by the present invention described below.